The present invention relates to an oxygen sensor which detects oxygen concentrations in measurement gas that flows in a pipe.
In recent years, there have been proposed and developed various oxygen sensors, and one oxygen sensor has been disclosed in Japanese Patent Provisional Publication No. 11-337513 (hereinafter is referred to as “JP11-337513”). In JP11-337513, an outside of a sensing element is covered with a protector, and this sensing element is inserted into an exhaust pipe with the sensing element covered in the protector. Then, these sensing element and protector are fixed to an inside of exhaust pipe such that exhaust gas flows into the protector from an inflow hole and touches the sensing element.